There are known portable objects, such as watches, equipped with sensors for detecting ultraviolet or UV rays. These devices include a semiconductor ultraviolet sensor consisting of a GaAsP component associated with a UV filter.
One drawback of these semiconductor ultraviolet sensors is that they have a lag time in the display and they are expensive. Moreover, because these sensors are electronic, it is undesirable to use them in a mechanical watch.
Another known possibility consists of a bracelet or watchband made of plastic, wherein said plastic includes a photochromic pigment, i.e. which changes colour with light. These photochromic pigments can be selected to be sensitive to different wavelengths, including ultraviolet wavelengths.
One drawback of this type of bracelet or watchband is that it is in a single colour and the variation in colour with the level of UV light is around this single colour. This means that a bracelet whose initial colour is green will vary in shade from a pale green to a dark green according to the intensity of ultraviolet light.
One drawback of this type of product is that the indication is not precise since it is difficult to associate a specific shade with a level of ultraviolet light.